1. Field of the Invention
This invention relates to membranes useful for resisting the formation or propagation of cracks in concrete slabs and foundation walls; for stabilizing, rehabilitating and relieving stress around cracks and joints in such slabs and walls; and for forming a permanent seal against the migration of moisture, insects, pesticides, gases and toxic contaminants through cracks and joints in such slabs and walls.
2. Description of Related Art
Architects and builders have long been aware of the need for keeping water and moisture away from underneath concrete slabs. Problems of indoor air quality and mold can be caused by moisture coming through the concrete slab. Additionally, toxic contaminants from pesticides and other chemicals, moisture vapor and insects can penetrate through joints and cracks in slabs. Cracks are frequently caused by factors such as settlement of the base, structural stresses from the building, expansive soils, freeze/thaw cycling, thermal expansion and contraction, and loads from building contents, occupants and vehicles. In some cases, cardboard-based products have previously been used under slabs poured over expansive soils. When wet, the cardboard will rot away to create stress-relieving voids. However, if the cardboard remains dry, it will not rot away and its capability for relieving stresses is reduced significantly.
To prevent moisture penetration, designers have also used “vapor barriers,” which generally have been rolls of polyethylene film, usually about 6 mils thick, rolled out with the slab poured over it. Over time, numerous problems have been experienced with such barriers. Conventional vapor barriers often get torn apart by construction activities and traffic, rendering them ineffective. They are also often torn and punctured by base settlement, building movement, joint movements, and cracks occurring in the slab above. Few conventional vapor barriers comprise a material that will adhere to a concrete slab poured on top. As a result, there has been growing concern in recent years with indoor air quality, flooring delamination and mold, which is sometimes referred to as the “sick building syndrome.”
Materials suppliers have responded with thicker vapor barriers (e.g., 10-46 mils), some with improved stretch properties. Most of these vapor barriers are not adhered to the underside of the slab. One of these suppliers offers a thicker vapor barrier (32-46 mils, including adhesive) incorporating an adhesive which creates a chemical bond to the concrete slab when the slab is poured. However, although these improved vapor barriers are proven by lab tests to be more resistant to tearing and puncturing, they do not have a long track record proving that the increased thickness and puncture resistance are sufficient to withstand the stress of construction and long term building operation. Moreover, they have no effect on reducing the amount or severity of the slab cracking.
More recently, other materials have been disclosed for use in various ways for waterproofing, for protecting foundations, for improving subsurface drainage, and for subgrade stabilization. Such materials include, for example, rubberized asphalt or bitumen in the form of a thixotropic liquid or membrane. Bitumen is often modified with plastomers or elastomers to give it better stability and durability. Multilayered composite sheets consisting of an exceptionally tough high density polyethylene film, a synthetic pressure-sensitive adhesive and a protective coating are marketed as waterproofing membranes by Grace Construction Products, a division of W.R. Grace & Co. In particular, membranes marketed under the trade names “Preprufe 160” and “Preprufe 300” have thicknesses of 1.07 mm (42 mils) and 1.42 mm (56 mils), respectively. W.R. Grace & Co. also markets a composite sheet of rubberized asphalt and cross-laminated polyethylene film under the trademark Bituthene® 3000. This material, which has a total thickness of about 1.5 mm, is recommended for all horizontal and vertical waterproofing of structural concrete above and below grade.
Highway engineers have long used highway underseal membranes during pavement rehabilitation. A typical application is to install highway underseal membranes over joints or cracks of the old pavement being rehabilitated, then to install a new layer of asphalt pavement over the old pavement. The departments of transportation in a number of states have documented research showing that the use of highway underseal membranes consistently reduces both the amount and severity of cracking in the new pavement layer installed above it. These reports generally attribute the reduction in cracking to the stress relief property of a rubberized asphalt component in the highway underseal membrane.
Although highway underseal is not known to have been used to reduce cracking of concrete slabs, the stress-relieving properties of rubberized asphalt have been used in building construction for the purpose of reducing cracking in ceramic tile floors. In this application, the product, often referred to as “anti-fracture membrane” or “crack isolation membrane” is installed over the floor substrate (generally concrete or wood), which is to receive the ceramic floor tile. On top of the anti-fracture membrane is installed a setting bed (usually latex modified) and then the ceramic tile. There is a growing acceptance among building designers and contractors that the use of anti-fracture membrane reduces the amount of ceramic tile cracking by relieving stress created by cracking or movement of the floor substrate underneath the tile.
Woven and nonwoven geotextiles comprising polypropylene, polyester, high density polyethylene and nylon have also been recognized for use in soil stabilization and reinforcement, for erosion control, and for preventing infiltration of fine particulate soils into gravel drains, perforated piping, and the like. Geotextiles are strong, durable and chemically inert materials that are said to be virtually unaffected by the effects of ground conditions, weather and aging, and are commercially available in either woven or nonwoven form. Nonwoven geotextiles can comprise long, continuous filaments that are thermally bonded, or short staple fibers that are bonded by a needling process.
More recently, nonwoven geotextiles have been disclosed for use with bitumen membranes. Parchem Construction Products Pty Ltd of Wyong, New South Wales, discloses reinforced bituminous sheet membranes that are applied with a torch and are marketed for applications such as foundations, basements, tunnels, roofs, etc. The membranes are reinforced with a non-woven, continuously extruded, spunbonded polyester fabric that is said to be rot proof, resistant to heat, aging and puncture, and have excellent elongation. The disclosed sheets are said to have thicknesses ranging from about 3 to about 4 mm, or 4.5 mm with a mineral finish. The lower face of the membrane is made with a sacrificial polyethylene film that prevents sticking during storage and is rapidly burned off with a torch during installation.
American Colloid Company has patented in U.S. Pat. No. 5,389,166 a water barrier formed from a clay-fiber mat, and related method. The University of Illinois has patented in U.S. Pat. No. 6,518,330 a multifunctional, autonomically healing composite material comprising embedded capsules that release a healing agent into a crack plane when damage occurs. The healing agent is polymerized by contact with an activator to bond the crack faces. The technology is disclosed for use in applications ranging from microelectronics to composite airplane wings.
Notwithstanding the materials and products that have previously been disclosed for use in waterproofing concrete walls and slabs, and for blocking and stabilizing cracks occurring in such walls and slabs, there remains a need for a membrane that is strong, durable, readily attachable to concrete, relatively inelastic, and substantially impermeable to pooled or migrating groundwater or moisture vapor.